Electronic devices for the power supplies or other applications are conventionally provided in a protective, heat-dissipating package. Often, the device (e.g., a metal oxide semiconductor field-effect transistor, or "MOSFET") is attached to a lead-frame by a wire bonding technique. The device is then encapsulated or "molded," wherein an encapsulant is formed about the device to yield a unitary, board-mountable package device. One well-known configuration for board-mountable package is a so-called dual in-line package ("DIP"), wherein electrical leads protrude from opposing sidewalls of the package. The leads are advantageously so arranged to allow the package to be mounted to a circuit board by various conventional soldering processes. DIPs are widely used for packaging integrated circuits, most often in telecommunications or computer related environments.
In a power electronics environment, the packaged power devices are conventionally mounted directly to a circuit board, using either through-hole or surface-mounting techniques. The devices are then joined with other electronic components to form a circuit, perhaps to function as a power supply such as a DC/DC power converter.
As with other types of electronic components, the trend in the design of power supplies has been toward achieving increased power and device density and lower device profile. However, any improvements in power, density and profile cannot be at the expense of the thermal and electrical characteristics of the components and overall power supply.
Analogous to the packaged power devices, the power supply is conventionally encapsulated to form a packaged power supply module. Using the DC/DC power converter as an example, a simplified process of constructing the packaged DC/DC power converter will hereinafter be described. First, the packaged devices (e.g., power switching devices) of the DC/DC power converter that must be thermally managed due to high power dissipation are mounted via an insulator to a five-sided metal enclosure. Next, a printed circuit board including the remaining components (e.g., a transformer, inductor, output filter and control circuitry) of the DC/DC power converter is placed over the packaged switching devices in the metal enclosure. The printed circuit board Is then mechanically fastened to the enclosure and the leads of the packaged switching device are soldered to the printed circuit board. Third, an encapsulant is flowed into the enclosure covering the packaged switching devices and circuit board with leads exposed therefrom for connection to a circuit employing the DC/DC power converter to advantage. Finally, the encapsulant is cured (e.g., through exposure to heat) thereby forming a packaged power supply module.
While the aforementioned technique provides a viable alternative for packaging a power supply, it endures several limitations. First, the metal enclosure is electrically conductive thereby creating an environment where the components of the power supply must be individually isolated therefrom. Second, the thermal and electrical characteristics of the devices therein are unacceptable, namely, the thermal resistance of the power devices is high. In conjunction therewith, the power supply module employed discrete devices and did not incorporate planar magnetic devices into the design. Third, the package density of the power supply module is low. Thus, in a period where the trend is toward higher power density power supply modules, the foregoing design for packaging the power supply module is contrary to the present trend and provides a lower power density package. Finally, the design requires several iterative manual steps that do not support a cost effective and mass producible design for power supply modules.
Accordingly, what is needed in the art is a power supply and a technique for packaging power supply circuitry into a packaged power supply module that enhances the power and device density of the power supply without sacrificing the thermal and electrical characteristics of the devices. Preferably, the technique should be cost-effective and suitable for mass production.